Which of the following statements is false? Group of answer choices A) Dissolved gases such as nitric oxide (NO) can act as signal molecules, but because they cannot directly activate intracellular proteins they must act by affecting membrane lipids. B) Nucleotides and amino acids can act as extracellular signal molecules. C) Some signal molecules are transmembrane proteins. D) Some signal molecules can bind directly to intracellular proteins that bind DNA and regulate gene transcription.

ATP is made of adenosine (a type of nucleotide) and used in cell signalling called "purigenic signalling" and amino acids are also used as signal molecules.

C) Some signal molecules are transmembrane proteins:

Transmembrane acts as receptors for smaller signal molecules so this can also be accepted as true.

D) Some signal molecules can bind directly to intracellular proteins that bind DNA and regulate gene transcription:

That is also true, some of the hormones can cross lipid membrane of the cells and bind directly to the intracellular (inside-of-a-cell) proteins.

Lastly; dissolved gasses such as nitric oxide can activate proteins such as guanylyl cyclase so this choice is false.